The Null Hypothesis
by Docnerd89
Summary: Castle has a theory about unconvincing people who are convinced he and Beckett are in a relationship, and convincing them that they're not, by disproving whatever proof they have which stands as the foundation to their hypothesis that they are in a relationship.
1. Chapter 1

-1-

"That's it," Castle yelled, propelling himself off his perch next to her on her desk, scaring a few years out of her. "This is ridiculous."

"You're ridiculous," Kate hissed at him in disdain, before gathering herself. "But what, dare I ask, are you talking about?"

"Us being together," he said plainly.

She looked at him like he'd grown two heads, one of which was purple and had antennae. "We aren't together."

"I know that."

"I should hope so."

"And you know that. But how many times have we had to clear it up?"

"One time too many."

"Exactly. Yet people accuse us of being together."

"Castle, I feel vaguely offended that you're genuinely frustrated about this. Possibly more than I am."

"I _am_ frustrated."

He really was! But he wasn't about to tell her why. Castle's reasons were none too noble. The source of his frustration was her frustration. When people kept reminding her of their non-relationship, they were also unknowingly reducing his chances of making her forget that she didn't not want a relationship. Why didn't people understand, for crying out loud?!

"Ohhhkay," Kate drew out.

"We should do something about it."

"You want to stop harassing me?" she said with a ridiculously cheesy grin.

If he didn't know her the way he did, he'd be upset. But he did know her. If she was serious, he'd probably convince her otherwise anyway. Something they had already been through. In short, he wasn't worried. "Woah now! Do I want to stop breathing? Kate Beckett, don't be ridiculous."

"A girl could dream."

"Oh. What kind of dreams? Are they raunchy? Do they involve a certain ruggedly handsome author?"

"As if I'd tell you. No. And you wish."

"I do wish. I so do wish," he said, nodding so hard he was getting dizzy.

"Castle, focus?"

"Right. I have a plan."

"Why am I not surprised?"

"Because you have come to realize my brilliance."

"I used to think you have a big ego. Oh, how I underestimated it."

"Do you want to hear the plan?"

"Are you going to leave me alone until I do?"

"What do you think?"

"Get on with it, then."

"I propose we prove ourselves."

"How do we prove we don't have a relationship?"

"We keep denying its existence, but nobody believes us. Why?"

"What do you mean 'why'?"

"Why don't people believe us?"

"Because -," Kate tried to think, coming up short. Could it be that Castle actually had a point? Nah. "Because people are stupid."

"No, my lovely Detective. It's because they don't have a reason not to not believe us."

"Did you hit your head while we were chasing that suspect today?"

"Yes, but that's besides the point. See the people who believe we're in a relationship have seen or heard something to convince them."

"Okay."

"And we have to unconvince them."

"You're finally starting to make a little sense."

"For that we have to know what has them convinced. We find their hypothesis, upon which they have established our relationship, and provide them with the alternative hypothesis to prove the non-existence of said relationship."

"Ah, I see," Kate nodded, as he beamed at her. "Now can we get back to work?"

The smile dropped off his face, and his shoulders sagged. She was trying hard not to simultaneously sock him and laugh at him.

"Beckett!" Castle whined.

She sighed. "Yes, Castle?"

"Did you not hear all of that?"

"I spent a precious few minutes and brain cells on it, all so you would let me get back to this _murder_ we're trying to solve, and possibly join me if you could spare your brilliant mind to such a mundane task."

"Aww, Beckett. You think I have a brilliant mind?" he said, sitting back down next to her as she rolled her eyes at him.

She was lucky Castle could be so easily distracted. Or so she thought.

* * *

Kate had forgotten all about Castle's weird plan, if it could be called that. She thought he'd forgotten about it too. That is, until one particularly quiet afternoon at the precinct.

Castle had the habit of disappearing for periods of time so it strangely coincided with Beckett having to do paperwork. Usually, though, he would either tell her he's going home, or he'd bug Esposito or Ryan, or distract some other poor unsuspecting fool. More rarely he'd sit with Montgomery in the name of research. In any case, he always touched base, and made sure not to go more than twenty minutes without bugging her.

And so when it had been an hour and a half of peaceful paperwork completion, Kate knew something was up.

She tossed a scrunched up piece of waste paper at Ryan, hitting him squarely in the forehead. "Ryan, you seen Castle?"

Ryan blinked, and looked around. As if she hadn't done that already. "Um. No. Haven't seen him in a while now. Where is he?"

She rolled her eyes. "I don't know. That's why I'm asking you."

"Miss your boyfriend already, Beckett?" Esposito piped up, looking proud of himself.

"Espo, I swear to God, I will come over there and - what?" What she would go over there and do, Espo never had the chance to find out, because he'd successfully spotted Castle and pointed to him wordlessly, his eyebrow raised in a mix of confusion and suspicion.

Kate had turned around expecting Castle to be heading towards her. Instead she saw his head and half his body poke out from behind a white board as he dragged it into an unused room. The grey room, as they had come to call it, was being refurbished after recently being damaged due to a water leak from the floor above. Really all that was left was for it to be painted and furnished, but funds were tight, and they were able to work without it, so there it sat, grey and unused.

"What's he up to? Kate asked, directing the question at no one in particular.

"Beats me," Ryan said, "he's your partner."

She bit her lip, wondering whether it was better for her sanity to pursue this, or let it go.

She decided to let it go.

Fifteen minutes later, she decided she couldn't let it go, and he'd long since messed with her sanity anyway. That was how she found herself in the grey room, watching Castle make a - a murder board of their relationship? And people called _her_ morbid.

"Castle, what are you doing?"

Castle squeaked and jumped two feet away from her, wielding his marker out like a sword. "Beckett. Hah. You almost scared me."

"Almost?" she smirked, crossing her arms and raising her well sculpted eyebrow.

"This is my plan."

"You're plan to - what exactly?"

"You know, my plan," he waved randomly at the board. "I told you about it already. You even actually listened to it."

"Huh?"

"My theory about unconvincing people who are convinced we're in a relationship, and convincing them that we're not, by disproving whatever proof they have which stands as the foundation to their hypothesis."

"Oh, that plan," she said, rubbing at her temple.

"Yep. So this is the null hypothesis," Castle said, pointing at the large red font.

"Castle, what the hell?"

"What?"

"This says, 'Beckett and Castle are in a relationship'."

"Yes, I know. I can read. Also, I wrote that."

"How is that supposed to convince people we're not in a relationship?" she said a little frantically. The man could drive her insane.

"Because this is the null hypothesis," he said, looking smug. "Does sound nice, doesn't it?"

"I'll tell you what sounds nice," she said, rolling her sleeves up as she advanced on him. He jumped off the plastic covered table rounding it so it stood between them.

"Woah, calm down."

"Richard Castle, do not tell me to calm down while you are spreading lies about our non-existent non-relationship."

"I'm doing the exact opposite. I'm trying to spread the truth about our existent - wait a minute, I think you said that wrong, because the opposite implies - OW!"

"You have two minutes to explain before I hit you where it really hurts."

Castle winced at the thought and nodded his acquiescence. "Fine. Won't even take that long. Have a seat," he said, fighting the urge to shield himself, and added, "please?"

Kate huffed, but sat on the table where he'd been sitting before. He sat down next to her so that their sides touched, even if the table was spacious enough to not have them invading the others personal space. There was dust on some parts of this one. A perfectly reasonable explanation for this plastic-covered hardly-used table. Not so much for her desk that they treated similarly.

"See, this is the null hypothesis. The hypothesis that other people are putting forth, and we are denying. Once we reject the null hypothesis, we thereby accept the alternative hypothesis, which is what we are trying to prove."

"That you and I are not in a relationship."

"Right."

"So we prove that, by disproving this?" she said, pointing at the board.

"Exactly."

"Okay, and how do we do that?"

"By letting people try to prove the null hypothesis."

"Isn't that counterproductive?"

"Not when we disprove their theories. Once we do, there's only the alternative that remains, and they'll finally accept it."

"That - actually makes sense."

"I can be sensible," he said, nudging her with his shoulder.

Kate couldn't help but smile, as she rested her head on his shoulder just for a moment. A slightly prolonged moment. "Careful, Castle. Or I'll expect you to be sensible more often."

He gasped. "Wouldn't want that. What a blip on my well maintained reputation."

"How ever will you recover?"

"I'll just have to be nonsensical more often."

Kate groaned as she straightened up, and pushed him off the table, laughing as he tried to bat away the dust off his bottom.

* * *

 **A/N:**

1) Thanks Bot, for having my back, as usual! You really understand my weirdo brain.

2) A Null and Alternate Hypothesis are actually scientific methods of determining the given hypothesis. I learnt it in biostatistics - a subject that I studied because it was mandatory. :| The way Castle is using it, is not quite how it works. BUT, what Beckett doesn't know, won't hurt Castle.

Cheers, and thanks for reading!


	2. Chapter 2

-2-

There were a lot of times where Castle didn't know what he was doing.

Like that one time he tried to cook a turkey without any instructions, beyond what he'd seen once on an Australian TV cooking competition. That didn't end very well for anyone involved, or anyone within splattering range.

There was that other time where he needed to help Alexis with a school project. He had no idea what he was doing with one of those home chemistry experiments. His darling daughter, bless her, was painstakingly following instructions, even as he got bored and started mixing the various solvents willy-nilly. It somehow led to the creation of shiny goop that she had an idea to use. She ended up winning and drawing him a Best Daddy Ever certificate, which he laminated for proof.

So yes, there were a lot of times Castle could think of where he didn't know what he was doing.

This wasn't one of those times.

He'd read about statistical hypothesis testing in an article once, and though he was usually more authentic about research for his books, he did suspend reality every now and then. Martha used to tell him that creativity was more important than intelligence. Of course that was usually when she wanted him to run lines with her for a bit. Didn't make it right or wrong.

Sometimes creativity meant taking risks. In this case, he'd managed to sell his 'plan' to Beckett. A feat that not only made him proud, but also gave him the niggling feeling that deep down in the depths of her irritated heart, she wanted to buy it.

Castle's agenda was pretty simple. He didn't know what to believe anymore. Were they in a relationship? Technically, no, Castle would say. Absolutely not, Castle knew Beckett would insist. But did he want to be? He thought he did. He felt it deeply. But hearing it from other sources - that he wasn't imagining the spark between them, would be good. He wasn't ordinarily insecure when it came to relationships, but this thing between them wasn't ordinary.

* * *

It seemed like the null hypothesis had become something of a precinct hot topic. A few, admittedly deserved, pinches led Castle to add his first note to the board, directly under the subject line.

 _Castle and Beckett are not in a relationship, but would like very much to know why everyone thinks they are. This is your chance to prove you're right; or ours to prove you wrong._

Five minutes after he'd put up the note, he saw another one pinned next to it.

 _This is all Castle's -_ _fault-_ _idea. - KB  
_ (The fault had been hastily scratched out)

After that she had gone back to doing what she did best - ignoring Castle, bantering with him, rolling her eyes at his ridiculous theories, cautiously listening to his genuine theories, finding reasons to express her violence at him. He didn't even mind the last one. She was also generally pretending that there was no grand plan currently under operation in the Grey Room.

Through the day, Castle watched as the news spread. The fellow detectives were abuzz. He even caught the janitor seemingly lost in his thoughts while stroking his imaginary beard. Huh.

Montgomery had been in the Grey Room, and had glared at him. But after Castle had clumsily rambled his plan out to him, well - he gave a wordless shrug and walked away. Castle swore to Beckett that the captain looked amused as he entered his room.

Later that day he saw Ryan dragging Esposito into the Grey Room, looking quite excited. Of itself, that wasn't too unusual. Ryan was totally his favorite. Things became more suspicious later, when Esposito more subtly got LT and Karpowski to join them. They were in there a solid ten minutes. What were they up to?

"Let's go, Castle."

"Yeah," he said distractedly as he stood to wear his coat. "Wait, go where?"

Beckett narrowed her eyes at him. "To follow up on the lead?"

"Oh, right. That."

"Uhuh," she said, raising her brow at him.

He tried to cover up. She would shut operations down quicker than the blink of an eye if she thought it was interfering with actual work.

"You want me to get Ryan and Esposito?" he offered innocently.

"No, I don't think they need to come along. Besides, they have to review the witness statements."

"Right, right," he nodded, pursing his lips while she got her gun and coat on. "Well then, I'll let them know where we're going. Just in case."

"Castle?"

It wasn't fair that she could convey so much simply by saying his name. Right now her inflection weighed heavy with suspicion, and the kind of knowledge that mothers inherently possess when they know their kids are up to something. Dammit.

"Yes, Beckett?" he said confidently, standing his ground. Avoiding her eyes, focusing instead on the cute little dimple in her brow. It was enough to distract him from feeling scared and showing signs of weakness. He hoped.

"Nothing. Go tell your boyfriends where we are so they won't worry. But hurry up."

He grinned at her, giving her two thumbs up before trotting off to the Grey Room.

By the time he got there, Karpowski and LT had already left. Castle saw Esposito pocketing something and Ryan scribbling in the little black diary he carried around.

"That's Karpowski down for January," Ryan said before Esposito nudged him.

"Boys."

"Castle," they said together.

A few seconds of awkward silence would have certainly gone on longer, but with Beckett waiting on him, Castle didn't want to waste too much time. As much as he liked suspense.

"You guys discussing your ideas about this?" he said, pointing to the white board.

"Uh. Yeah. We're just-," Ryan paused looking to Esposito for help.

"Putting together our timelines for certain events. Organizing our evidence," Esposito finished.

"Right," Castle said disbelievingly. He nodded to Ryan's book, "What's that?"

"Jotting down notes before I forget them. I like to be thorough."

"Uhuh. What's gonna happen in January?"

"Hasn't anybody ever told you it's rude to eavesdrop? Martha would be ashamed."

"Mother gave me lessons on eavesdropping. She'd probably be proud."

"Castle, you coming?" Beckett's voice cut off any further discussion.

"Yeah," he yelled back towards the elevator where she waited for him impatiently. "We're not done," he said, pointing his fingers to his eyes and then to theirs. They glared at him at first, but he thought he saw their shoulders sag in relief as he turned around.

If LT and Karpowski hadn't been in the mix, Castle's brain would be rife with theories about just why Ryan and Espo were sitting alone, secluded and secretive, in a little grey room for as long as they were. It was interesting nonetheless. A mystery for another day.

* * *

 **AN** : Thanks for reading!

Kindly note that this is not a prime example of how to use the hypotheses testing method. I claim creative license to misuse it as Castle pleases. Guest reviewer, maybe if you taught me, I wouldn't dislike the topic as much. Who knows? :)

About the double - meh - multiple negatives.. Like Castle, I knew what I was doing. Sometimes, in jest, it is fun to be annoying. :D Hopefully not too much.

Any ideas on what Rysposito are up to?


	3. Chapter 3

-3-

It was working.

The first few notes were on the board. He was drawn to the small piece of note paper taped in the upper left corner.

 _There was a moment today when Beckett looked unsettled. We usually leave each other alone in times like these. It's probably unhealthy. But Castle stepped up and asked if she was okay. She shared something with him, and later he left. While he was walking away, she had this sad smile on her face. Like she genuinely appreciated him. I think she does._

Castle smiled, reading the note. He thought he remembered the moment this anonymous contributor was referring to.

They'd had an interesting case today. Vampires!

The moment being eluded to was probably when Beckett had to inform Matthew Freeman's family of his death. He could see that it had troubled her. She looked so forlorn and - and complex, and beautiful. He knew he had it bad, but all he could see was the good in her, shining through. Her compassion as a person, and dedication as a detective.

" _It's the phone call that changes everything."_ Kate had said.

He knew that every time she had to do this - every time she had to inform the family, friends, loved ones - it broke her heart. It took her back to when she was informed, when she was on the other side. It was that tragedy that lent authenticity to her empathy. Her 'sorry's were weighed down by sincerity. Unjust, but true. He knew it made her work that much harder to bring closure to the victims, let them have peace in their lives - like she didn't have in hers.

All Castle wanted to do was sneak his hand across her back and tug her close, share his warmth. Kiss her temple, hold her hand. Comfort her. But he couldn't. And it took all his strength.

He offered to stay, and felt only slightly disappointed that she didn't want him there with him. Felt proud that she was so strong and brave. Every time.

He had to shake himself out of the melancholy seeping through the atmosphere and moved on to the next note. This one was by Esposito.

 _We interrupted a potential kiss today. - J.E._

There was a post it stuck on the note, seemingly by Ryan. It wasn't signed, but Castle recognized the handwriting.

 _But they denied it._

 _He didn't._

 _She did._

 _So you believe her?_

 _Oh no, they totally would've kissed if we didn't interrupt them. (Sorry, Castle!)_

On the one hand, he was amused. On the other, he wanted to scrunch the card and make Ryan and Epsosito eat it.

Castle sighed. They did have a moment today. Apparently two. He didn't even think of the first one as a moment, but it was, he realized. They had many such moments that just slipped by them, unacknowledged. The bigger picture was an amalgamation of all of these.

It wasn't a big secret, the way Castle felt about Beckett. God knows he'd even made passes at her early on. He'd stopped though. Out of respect, out of an instinctual need for self-preservation. He didn't know to what extent, but he knew he was serious about his feelings for her. But would Beckett trust those? Coming from him, maybe not so much. But coming from a whole lot of different people, most of whom she'd known for longer than him? Maybe. Maybe not.

Castle would never pressure her into a relationship. But he didn't think it was wrong to nudge her in a direction she wouldn't even accept exists. Would she go down the road? Only time would tell.

* * *

Over the next couple of days, Castle noticed two more notes. Much to his astonishment, one was from Lanie.

 _KB called me yesterday, told me to take a look at Castle's 'Vampire bite'. I asked her if she was the vampire. I was only teasing, like we do to each other all the time. She went really quiet over the phone and I had to call out her name twice before she replied with a soft, 'please?'. I told her that of course I would. Writer Boy was one of our own, I'd be happy to take a look. When I prodded her about it, because I found her behaviour unusual, her only reply before cutting the call was, "He could've gotten badly hurt, I don't know what -. Never mind. Thanks, Lanie, see you soon." She was slightly freaked out. I could tell._

The next was from Esposito.

 _Beckett was staring absently at nothing in particular. When I caught her eye and asked her what was up, she just shook her head, and went into the break room. She'd sat down, placed a saucer in front of her. Then she yanked out tissues and arranged them on the saucer and placed Castle's egg thing on it. I may have imagined that she stroked it once with her thumb, and then got back to work like nothing happened._

 _We were talking when Castle's call interrupted us. It was short, but she looked happier after it was done. I asked her later if everything was all right between her and Castle. She dismissed my concerns. Castle had informed her that there was some trouble with Alexis's friend, but that everything was okay. Then she directed the conversation back to the case._

 _The little egg thing? Beckett's a doer. I have a feeling she didn't know how to help directly. Didn't know if she should. So she did what she could._

* * *

It was a lot to digest. The simplest note so far had been the one about the interrupted kiss. Everything else was deeper. He wondered for the first time, if this would backfire on him. If it would scare her away, rather than convince her.

With trepidation he walked up to her desk. She was getting ready to leave.

"You okay, Castle?"

"Yeah, yeah. Beckett, have you seen the board?"

She turned to the white board next to her and back at him levelling him with a puzzled look.

"Um. Not that one, the other one," he said, pointing his thumb over his shoulder to indicate the Grey Room.

"Oh. No, I haven't. That little project is yours, Castle. I'm sure you're giving it due attention."

"You're not even going to look?" he asked, feeling both relieved and disappointed. Kate just smiled at him, looking happy and dare he think it, care-free.

"Sure I will. But not tonight. I'm finally getting the chance to leave early. I'm gonna take it."

"Grand plans?" he asked, simultaneously interested and wary.

"Grand plan to catch up on sleep."

"Ah. Well deserved R n R."

"Yup. I'll see you tomorrow."

"Sure, see you," he said, but stopped her when she'd turned and taken a step. "Hey, Kate?"

Something in his tone must have caught her ear. She took a step closer to him. He held her wrist and leaned in closer. They were suddenly alone, in their own private little bubble.

"Castle?"

"Thank you for asking Lanie to see the vampire bite."

"He wasn't a vampire, Castle," she said. She wanted to roll her eyes at him. To take down the intensity a notch. But he couldn't help it. It was sincere, and bursting through him. This appreciation for her concern.

They were both talking softly, though they probably hadn't realized it. Both lost in each other, realizing that there was something going on. Something had shifted. Tilted. At least he had an idea, but did she?

"All the same."

Her eyes dropped from his, as she nodded. He took the opportunity to lean in further and kiss her cheek. He heard the quick intake of breath, and watched her with heavy lidded eyes as she tried to breathe out slowly. Tried to regain her equilibrium, and gather herself to look him in the eyes again.

"Until tomorrow, Kate."

He took a step back, paused only for a second before he walked away, leaving her to regroup in peace. There was nobody around, he noticed as he walked to the elevator.

This wouldn't make it as a piece of evidence. An interpretation by romantics at heart, or a retelling by the observant. He loved that he was getting some proof beyond the workings of his lovestruck mind. But he loved even more that they had this. This stolen moment which would be their little secret.

* * *

 **AN** : And so it begins.


	4. Chapter 4

-4-

 _I've never seen Detective Beckett making goo-goo eyes at anyone before, so imagine my surprise when this was directed at Castle. Of course, seeing Castle and Alexis interact would melt anyone's heart, but it still surprised me. I gave her a knowing look, and judging by the way she turned away to hide her blush and compose herself? Well, I didn't make Captain without knowing a thing or two about people._

The Captain posted a note? Well, hot damn!

 _He kills her patience? I don't believe it. Not for a second. None of us do. - J.E._

And another one.

 _They shared chocolate. Just saying. - K.R._

 _Oh yeah, I saw that, too. - J.E._

 _What does that have to do with anything? - L.P._

 _Chica, sharing chocolate is the edible way to say -_

The rest was scratched off. Very thoroughly. Probably by Lanie if Castle had to guess. Curious.

Thing is, Castle wished for all of it to be true. For everything being said, being posted on this board, to be true.

And then he realized it was. He thought back to all the times that he didn't realize the truth for what it was, and it scared him. To realize it now - the epiphany felt like a sucker punch to the heart. It was so strong.

So strong.

When they'd found Hayley's sister, Sky, Beckett worked her magic. She reassured her. In doing that, she had to dig deep inside herself. Something that Kate Beckett always did. Something that he had to work so hard to capture when he wrote Nikki. He was proud of Nikki. He was proud and then some, of Kate.

Watching her interrogate Bree Busch as he stood next to Montgomery, like all the other times he'd watched her in an interrogation, was inspiring. Inspiring for his writing. And yet another reason to - to add to his ever growing list.

 _You know how I know that she cares about him more than she lets on?_

 _She listens to him._

It wasn't signed. It wasn't a handwriting he recognized.

They mustn't know what they're talking about, though. She doesn't listen to him. She thinks he's nuts most of the time. Right?

Right?

But maybe she does.

Like when they were interrogating Ian. Ian Busch was justifying killing Hayley. Saying that _she_ _seduced him_. He had no idea - none - how badly Castle had wanted to snap his neck. This filthy piece of dirt that should have been looking out for her, protecting her.

His fists were balled up on his thigh as he spoke to Ian. The hatred must have been radiating off him.

That's when he felt it. The lightest brush of her pinky, running over his wrist to his thumb. It was swift. There and gone. He didn't need to look at Kate, knew she wouldn't be looking at him either. Her touch had settled him.

She listens to him.

In more ways than one.

He shook himself to look at the last note, beyond stunned to see it was from his mother.

Really?

 _Now, I know I've raised my Richard to be a gentleman. He walked her home after the concert last night. I hope he wasn't too much of a gentleman, if you know what I mean._

It was signed in her beautiful cursive signature.

The need for facepalming was overwhelming.

He was so a gentleman.

* * *

Castle blew out his candle and turned to face Martha and Alexis more fully. "Mother, could you take Alexis home, I'm just going to walk Kate to her place and get a cab back home."

"Of course, darling."

"Oh, Castle that's not necessary. I live close enough."

Castle completely ignored her, save for rolling his eyes at her and turning back to Alexis.

"Night, Pumpkin. See you soon."

Alexis hugged him, and they bid their goodnights and goodbyes.

"Honestly, you'd think chivalry would be slightly more appreciated, Beckett," he said, tsk-ing at her.

She bit into her lip in that way that drives him crazy, released it in a way that drives any thoughts straight out of his mind. "Well, Castle. I guess I wouldn't want you to lose your Chivalrous Men Club Card."

He beamed at her as he offered up his arm, and even more when she wound hers through it. If he pressed her a little close to his side, it was only because the night was a cold one.

"Castle?"

"Hmm?"

"You're a good father."

For some reason, he didn't turn to look at her. Didn't think he could take looking at her in just that moment without doing something stupid on a cold, beautiful, quiet night, after they'd spent it together listening to teenage angst-ridden, romantic music.

"You're a good daughter," he whispered back, feeling her hold on his arm tighten a fraction.

She was quiet as they walked along. He had a feeling she'd known why he said it. But his bumbling babbling mouth couldn't quite stop.

"When you said earlier, about Sky having to want to get clean, you knew what you were talking about."

She didn't reply, and he didn't push. Not more than he already had. They'd walked a couple of blocks, and he knew it was just a matter of a few minutes that he'd have to say goodnight. Perhaps even apologize.

In the little distance that remained, she seemed to find her voice. "Yeah, I knew what I was talking about."

They were at her building, Kate already climbing the first step. She stumbled as she turned around to face him.

His arm shot around her waist, pulled her to him. To steady her.

"I'm sorry," he said, his words falling to her cheek.

"Don't be. You caught me," she whispered back to him, her lips skimming his cheek in return.

"That's not what I meant," Castle clarified, every little hair in his stubble alive and on fire from her phantom of a kiss. He pressed infinitesimally closer, her scent intoxicating him.

"I know," she said, looking him in the eyes as she pulled away. "Goodnight, Castle."

"Until tomorrow, Detective."

She really was a mystery to him sometimes.

* * *

 **AN:** Sorry about the delay! Real life, you know. Meh. **  
**

...Season 2 is so awesome! I'm glad I'm using this as an excuse to rewatch it. Hehe.


End file.
